Color beveled nurbs path according to the x-y-direction in the final camera view
That's a beautiful node setting. I will try to explain some problem first:




You shouldn't use emission shader for your output, if the output is Color and you want that color directly show on your screen, please directly connect the Color socket to Output Surface socket. This post elaborated more detail of color output setting
What you mean too fast? Human color perception is complicated, we try a lot, a lot of method to describe and organize color: sRGB, Adobe RGB, NTSC, CMYK or even Pantone&reg;. Blender using sRGB as default output color and if my memory is correct, purple will be strongly receive for our eye in normal sRGB situation, Blender is using this solution as standard.






Back to your question:


Change the color management in properties panel, View Transform: Raw
Not sure, emission is useless in your situation, and the final subtract node can be done by changing the HSV node color
Directly connect the color to the output surface socket should fix the problem. Emission is not final color output for Cycle and EEVEE.